Description: (Taken directly from the application) The overall goal of this project is to seek a safe alternative to potassium citrate in normocalciuric nephrolithiasis. This goal will be pursued by obtaining validation of the efficacy and safety of K-Mag in an already completed randomized trial, and show that this treatment is particularly effective in normocalciuric patients than in hypercalciuric patients. Thus, a multiclinic, placebo-controlled randomized trail will be conducted with K-Mag. Participating patients will be those with recurrent calcium nephrolithiasis suffering from uncomplicated calcium stone disease who have recently undergone extracorporeal shock Wave Lithotripsy (ESWL) for removal of stones. Both normocalciuric and hypercalciuric patients will be enrolled. The treatment outcome will be analyzed by survival probability (percentage of patients remaining stone-free). The project will test the hypothesis that: 1 K-Mag would be more effective than placebo in inhibiting stone formation in both normocalciuric and hypercalciuric patients, 2 The response of normocalciuric patients K-Mag would be superior to that of hypercalciuric patients, due to the pathogenetic role of hypercalciuria, and 3 The propensity from recurrent stone formation is unaffected by ESWL, thus emphasizing the importance of medical management.